I've just been asked to play for my first wedding.

Tim, I feel the most important thing to be concerned about is how confident you look, and how confident you feel. People will accept a wrong note, or a wrong button, in fact most of the time there in their own world doing what they do at gatherings. But when you lose my confidence, you lose control, that they will hear and feel.

Price is not to important here, although people do judge by what you are charging. I remember when I was going to homes teaching guitar, I bought some new clothes, then I bought a new car---then I raised my the cost of the lesson. They loved it, they bragged about this fine teacher that comes to their home.
Tim, treat it like a game. go to the job and enjoy it. That'll be the best you can do, and they will love it.

Relax and enjoy, John C.